Pharmacokinetics in plasma and alveolar regions of a healthy calf intramuscularly administered a single dose of orbifloxacin

This study analyzed the pharmacokinetics of orbifloxacin (OBFX) in plasma, and its migration and retention in epithelial lining fluid (ELF) and alveolar cells within the bronchoalveolar lavage fluid (BALF). Four healthy calves received a single dose of OBFX (5.0 mg/kg) intramuscularly. Post-administration OBFX dynamics were in accordance with a non-compartment model, including the absorption phase. The maximum concentration (C_max) of plasma OBFX was 2.2 ± 0.1 μg/ml at 2.3 ± 0.5 hr post administration and gradually decreased to 0.3 ± 0.2 μg/ml at 24 hr following administration. The C_max of ELF OBFX was 9.3 ± 0.4 μg/ml at 3.0 ± 2.0 hr post administration and gradually decreased to 1.2 ± 0.1 μg/ml at 24 hr following administration. The C_max of alveolar cells OBFX was 9.3 ± 2.9 μg/ml at 4.0 hr post administration and gradually decreased to 1.1 ± 0.2 μg/ml at 24 hr following administration. The half-life of OBFX in plasma, ELF, and alveolar cells were 6.9 ± 2.2, 7.0 ± 0.6, and 7.8 ± 1.6 hr, respectively. The C_max and the area under the concentration-time curve for 0–24 hr with OBFX were significantly higher in ELF and alveolar cells than in plasma (P<0.05). These results suggest that OBFX is distributed and retained at high concentrations in ELF and alveolar cells at 24 hr following administration. Hence, a single intramuscular dose of OBFX (5.0 mg/kg) may be an effective therapeutic agent against pneumonia.